Python 2.7 quick reference

13.1. Using the bytes type in 3.x
conversion

Versions 2.6+ support a new notation: to create a literal of
type bytes, place a “b” just before the opening quote.

>>> s = b'abc'
>>> s
'abc'
>>> type(s)
<type 'str'>

Such literals are exactly like regular string literals. The
difference comes when you convert your program to the 3.x
versions. In Python 3.x, a string of the form b'...' will have type bytes, which
will be different than the str (32-bit character)
type in 3.x.

One step in converting your 2.x programs to 3.x is to
add this import before all the other imports in
your program:

from __future__ import unicode_literals

In programs that start with this declaration, all string
literals will automatically be considered unicode type without using the u'...' prefix. This
means you may also include escape sequences of the form '\uXXXX', each of which
designates a 16-bit Unicode code point as four hexadecimal
digits XXXX.

Here is a demonstration of the difference. Before the import, the \u escape is not
recognized, and the value has type str.
Afterwards, the return value is type unicode